Molna masa(M) je omjermaseimnožine tvaria izražava se u gramima po molu (g/mol):[1]
![{\displaystyle M={\frac {m}{n}}}](https://wikimedia.org/api/rest_v1/media/math/render/svg/32398a386cca20dcc0e938544d13e9742e073d6c)
Molna masaneke tvari je masa 1 mola te tvari, odnosno masa čestice te tvari (ma= masa atoma,mf= masa molekule),
pomnoženaAvogadrovom konstantom(NA):
![{\displaystyle M={m_{a}}\cdot {N_{A}}}](https://wikimedia.org/api/rest_v1/media/math/render/svg/5707794ca7ecc514422870b3a8722c4bfaff1e13)
![{\displaystyle M={m_{f}}\cdot {N_{A}}}](https://wikimedia.org/api/rest_v1/media/math/render/svg/02536bcfc03d65549bed15645527053d437a4a76)
![{\displaystyle N_{A}=6,022\cdot 10^{23}\quad mol^{-1}}](https://wikimedia.org/api/rest_v1/media/math/render/svg/13054fb87e40f53ad4137753ca47de9079a3ee46)
Molna masa bilo koje tvari sadrži Avogadrov broj jedinki (atoma, iona, molekula), dakle N = 6,022*1023jedinki.
Molna masa je brojčano jednakarelativnoj atomskoj masiza atome irelativnoj molekulskoj masiza molekule uz dodatak jedinice g/mol:
![{\displaystyle M=A_{r}\quad \mathrm {g/mol} }](https://wikimedia.org/api/rest_v1/media/math/render/svg/1ceb33abd0f6e94931bf180ee64268127b2c696d)
![{\displaystyle M=M_{r}\quad \mathrm {g/mol} }](https://wikimedia.org/api/rest_v1/media/math/render/svg/3d535a014e1f43c4d9f4ea24cb1866a23a371fbf)
Molna masa je stalan i važan podatak za svaku elementarnu tvar ili spoj te se nalazi ispisan na naljepnici posude u kojoj se čuva.
![{\displaystyle M\mathrm {(Cl_{2})=?} \qquad M\mathrm {(Cl_{2})=[2A_{r}(Cl)]\ g/mol=[2\cdot 35,45]\ g/mol=70,90\ g/mol} }](https://wikimedia.org/api/rest_v1/media/math/render/svg/9fa747a2af1224815834612e24475da6832b020d)
Molna masa ugljikova dioksida:[uredi|uredi kôd]
![{\displaystyle M\mathrm {(CO_{2})=?} \qquad M\mathrm {(CO_{2})=[A_{r}(C)+2A_{r}(O)]\ g/mol=[12,0111+2\cdot 15,9994]\ g/mol=44,0099\ g/mol} }](https://wikimedia.org/api/rest_v1/media/math/render/svg/88d3b1c3ab17e1afd8c5e09904d74f4407ef0084)
![{\displaystyle M\mathrm {(CuSO_{4}\cdot 5H_{2}O)=?} \qquad M\mathrm {(CuSO_{4}\cdot 5H_{2}O)=[A_{r}(Cu)+A_{r}(S)+9A_{r}(O)+10A_{r}(H)]\ g/mol=249,685\ g/mol} }](https://wikimedia.org/api/rest_v1/media/math/render/svg/ae699051104da8134c4dd912318377af2d2c8388)
Habuš, Tomašić, Liber:Opća kemija 1: Udžbenik kemije za prvi razred gimnazije,1. izd., Profil, Zagreb, 2014.,ISBN978-953-12-1434-6,str. 138-140
- ↑[1]Institut za Hrvatski Jezik i Jezikoslovlje, Struna: Molna masa